Mario Laguna-Guerrero had been dating his 17-year-old girlfriend for two years and even lived with her and her mother before he made a decision that would change their relationship forever.

Laguna, struggling to repay a debt to smugglers who brought him into the country from Mexico, decided to become a pimp -- driving his girlfriend to migrant labor camps in Hillsborough County, Florida, and selling her for sex.

Over four months in late 2009, as many as 80 men slept with the teenage girl while Laguna pocketed $25 a head. He later pressured his girlfriend to recruit high school classmates to work as prostitutes too.

Law enforcement agents arrested Laguna in April and charged him with sex trafficking of a minor, a federal crime.

According to the affidavit, Laguna, 25, said his girlfriend, who's a U.S. citizen, agreed to help him pay off his debt by having sex for cash. But the girl, who has a mental disability and is only identified as "Victim #1," told detectives separately, "I don't wanna do this."

Investigators determined Victim #1 has an IQ of 58, which psychologists described to ABC News as "low-functioning," adding that she would have difficulties making decisions on her own.

"This girl was rescued from a nightmare which could only have gotten worse," said Hillsborough County Sheriff David Gee.

As national debate rages over ties between illegal immigration and crime, the Laguna-Guerrero case depicts a disturbing trend in human sex trafficking and, some immigration critics say, a consequence of the U.S. failure to secure its borders.

"This is a heinous crime, there are real victims left in its wake, and it's all unnecessary," said Ira Mehlman of the Federation of Americans for Immigration Reform. "It could have been prevented if he weren't here illegally... Legal immigrants go through a vetting process that's designed to weed out criminals."

Laguna, who worked as a strawberry picker on a farm near Tampa, first arrived in the U.S. in 2002. He told investigators the smugglers who brought him into the country threatened to cut off his fingers if he did not soon pay his $2,000 debt.

While Mehlman praised Immigration and Customs Enforcement agents for uncovering the case and prosecuting the "most egregious" crimes perpetrated by immigrants, he said more must be done to curb the "disproportionate" criminal activity of those in the U.S. illegally.

Are Immigrants Disproportionately Criminals?

Illegal immigrants make up about 3 percent of the U.S. population, according to Census statistics. "Criminal aliens" make up about 27 percent of inmates in federal prisons, according to a 2005 Government Accountability Office report.

But immigration advocates say focusing on the share of inmates in federal prison and on cases like Laguna's can be highly misleading and downright wrong.

"Immigrants are less likely to commit crimes than native-born citizens," said Ben Johnson, executive director of the American Immigration Council.

Johnson said the share of immigrants in federal prisons may seem alarming but that only 8 percent of all U.S. prisoners are in such facilities. Most are in state and local prisons, where incarceration rates for immigrants are lower than average.

He also pointed out that many immigrants in the federal system may simply be there because they lack legal immigration status -- not for having committed flagrant criminal offenses.

"No community is immune from the ravages of drugs and sexual violence. But the overwhelming majority of those crimes are not done by immigrants," Johnson said. "We don't ask criminals about their political affiliation or their religion. So why should we focus on their immigration status?"

Immigrations and Customs Enforcement officials say they continue to prosecute crimes committed by immigrants, including cases of sex trafficking. The agency investigated 557 sex trafficking cases between 2005 and 2007 and convicted 129 offenders, according to the most recent data.

Sex trafficking, or the recruitment, transportation and use of another person for the purpose of trading sex for money, has become an alarming trend in recent years.

An estimated 240,000 American children are at risk of commercial sexual exploitation with the average age of first-time prostitutes ranging from 12 to 14, according to a recent Justice Department study.

Laguna-Guerrero, who allegedly began trafficking his girlfriend when she was 16, currently faces a trial in U.S. Federal District Court. If convicted, he faces up to life in prison.